The abuse of alcohol and nicotine costs the US over 500 billion dollars annually and co-use of these drugs is common, with prevalence rates of 60-90% in alcoholics. One putative cause underlying this co-use is that alcohol and nicotine reciprocally increase the reinforcing efficacy of each other when both are concurrently available. However, experimental evidence of this type of interaction is limited. Research clarifying this interaction could have important implications for prevention, treatment and a FDA tobacco control policy that aims to reduce population use of tobacco products (and therefore nicotine consumption) to improve public health. To the extent that nicotine and alcohol are economic complements, FDA policies that reduce tobacco consumption could have the beneficial side effect of also reducing alcohol consumption. On the other hand, alcoholism and smoking are co-morbid disorders, suggesting that alcoholics may be a vulnerable subpopulation of smokers that would be more resistant to tobacco control policies. Animal models of drug self-administration provide an avenue to clarify this issue by assessing how consumption of these drugs changes during co-use. The proposed research will fill gaps in the literature by examining how nicotine and alcohol (ethanol) alters the reinforcing efficacy of each other when available alone or within a choice context. Specifically, convergent behavioral economic approaches will be employed to assess the hypothesis that ethanol and nicotine each enhance the demand for (i.e., reinforcing efficacy of) the other when concurrently available versus alone, and that they function as economic complements. The proposed studies will: 1) establish a dose-response curve for the effects of nicotine and ethanol on progressive-ratio (PR) breakpoints (i.e., reinforcing value) for the other drug (e.g., nicotine on ethanol intake and vice versa) or for food (control condition) and 2) determine how co-use alters demand for each drug and examine the nature of the economic relationship between drugs (e.g., complements, substitutes, etc.). Results will serve as preliminary data for an R01 proposal to begin addressing the following long-term goals of the present project: First, to assess how ethanol alters the reinforcing threshold dose of nicotine. Second, to model vulnerability factors for co-use in different populations, such as alcoholics, adolescents and across different sexes. Lastly, to examine how adolescent exposure to ethanol and/or nicotine impacts the etiology of ethanol and nicotine dependence and their co-use.